Emerald Ash Borer Infestation of White Fringetree Found to be Widespread

The emerald ash borer (Agrilus planipennis) is an invasive pest that is decimating ash trees across the United States and Canada. By 2019, it’s estimated that the beetle will have caused economic damage to the tune of $10 billion.

“After observing the condition of nearly 100 ornamental white fringetrees, I now expect that the majority of white fringetrees faced with sufficient pressure from emerald ash borer will get infested to some extent,” Cipollini said. “I’ve seen trees that have been killed by this or had parts of them die.”

Furthermore, emerald ash borer adults were observed emerging from branches of trees that were infested in the field and brought back to the laboratory.

“We’ve now done additional tests with stems of trees that we collected in the field,” Cipollini said. “When you directly place the eggs of the beetle on white fringetree in the laboratory, you get well-developed larvae back out.”

White fringetree is a close relative of ash. It is native to the United States, grows wild from New Jersey to Florida to Texas, and is increasingly being used as an ornamental tree in other parts of the country.

Concerned that the emerald ash borer could utilize other related tree species, Cipollini also studied how the insect fared on the Chinese fringetree (Chionanthus retusus), the Asian congener of white fringetree, and devilwood (Osmanthus americanus), an evergreen tree native to the southeastern United States that is related to the white fringetree.

Peculiarly, the beetles failed to successfully infest the Chinese fringetree. While the reason for failure is unknown, it might have something do to with evolution. The native range of Chinese fringetree in Asia overlaps with the range of the emerald ash borer, so the tree might possess bark defenses as a result of coevolution or selective pressures. One such defense might be the presence of bioactive phenolic derivatives hydroxytyrosol, oleuropein, and other iridoid glycosides, which have been shown to have anti-microbial and anti-insect effects in olive trees.

However, the emerald ash borer did show some evidence that it could survive, albeit barely, in devilwood. In the study, two larvae survived the ~40 day bioassay in the lab. The larvae were small, only one-seventh the size of the larvae on green ash, but they created galleries that approached levels that could be damaging to the tree.

“While its vulnerability to EAB would appear to be limited at present, devilwood is only the second species outside of the Fraxinus genus in North America that has been shown to support EAB larval development for such a long time,” the researchers wrote. “This indicates that different accessions, cultivars, and wild populations of the species studied here, as well as closely related … [species] are worthy of further scrutiny for their susceptibility to EAB.”